Also VMS qualifies as a fully memory-protected, preemptive OS:
The real innovation that Windows and OS/2 did was to take fully preemptive OSes and put them in marginal hardware (at the time) like PCs.
You are correct, but I was referring to desktops, and the particular example is Coherent from Mark Williams Company which was demonstrated running on an IBM PC at the National Computer Conference show in Houston in 1983. Minix came in 1987, if I recall correctly.
System V: https://en.wikipedia.org/wiki/System_5
BSD: https://en.wikipedia.org/wiki/BSD
SunOS: https://en.wikipedia.org/wiki/SunOS
Xenix: https://en.wikipedia.org/wiki/Xenix
https://en.wikipedia.org/wiki/Xenix (which was created by the eventually infamous Santa Cruz Operation - SCO - and licensed by Microsoft)
Also VMS qualifies as a fully memory-protected, preemptive OS: The real innovation that Windows and OS/2 did was to take fully preemptive OSes and put them in marginal hardware (at the time) like PCs.